Robust, highly conductive, and inexpensive proton exchange membranes (PEMs) are needed for practical and reliable electrochemical cell, e.g., fuel cell, operation at elevated temperatures. Current fuel cell membranes typically are based on polymeric materials, such as those available under the registered trademark NAFION® from E. I. duPont de Nemours and Co., Wilmington, Del., United States of America. A NAFION® polymer is a perfluorinated polymer comprising low levels of ionic groups, which aggregate to form ionic, hydrophilic clusters. These hydrophilic clusters allow transport of water and ions across membranes formed from NAFION® polymer, making it a useful material for fuel cell membranes, catalysis, and templating.
PEMs based on NAFION® polymers have long been considered benchmarks in terms of performance characteristics. See Heitner-Wirguin, C., J. Membrane Sci. 120, 1-33 (1996). Fuel cell membranes based on NAFION® polymer suffer several disadvantages, however. For example, NAFION® polymer is expensive and typically cannot be used in applications requiring temperatures in excess of 100° C. Also, the structure of NAFION® polymer is complex and not fully understood.
Further, the current class of PEM fuel cells, which typically operate at about 90° C., is hampered by sensitivities to carbon monoxide (CO) and peroxide formation that limit performance and require the use of high purity fuels. To overcome such sensitivities to CO, complex systems are required to remove CO from the fuel. Further, platinum catalysts typically are required on the anode to minimize the effect of CO on membrane polarization. A polymeric membrane capable of operating at elevated temperatures (e.g., temperatures above about 150° C.) would largely eliminate such concerns, because CO adsorption is no longer kinetically favorable at those temperatures.
Given the importance of practical operations of fuel cells with high performance, low cost, and extended lifetimes, various approaches to the synthesis and characterization of PEM materials have been reported. Doyle et al., J. Electrochem. Soc. 147, 34-37 (2001), have reviewed a number of alternative PEM systems, including polymer systems doped with acids or ionic liquids. Inorganic dopants and hybridization procedures also have been used in an effort to improve mechanical, thermal, and water sorption properties of NAFION®-based PEMs. See Deng. Q., et al., J. Appl. Polymer Sci. 68, 747-763 (1998); Antonucci, P. L., et al., Solid State Ionics 125, 431-437 (1999).
There exists, however, a need in the art for improved materials for PEMs, in particular PEMs for sustained operation in fuel cells at elevated temperatures (e.g., temperatures above about 120° C., or in some cases temperatures above about 150° C.).
Further, there exists a need in the art for improved fabrics, for example for use in breathable chemical and biological protective clothing for military personnel, emergency response teams, industrial and/or agricultural workers and other applications, and healthcare professionals. Standard protective clothing is made largely from butyl rubber (BR), a material whose impermeability provides an excellent level of protection, but also traps heat and moisture inside the garments. BR garments also are bulky and limit dexterity. For example, a particular problem with gloves made from BR materials is that they constrain hand movement. In a desert combat environment these problems could result in more than simple discomfort and inconvenience.
Thus, there is a need in the art for improved materials for use as fuel cell membranes and as a fabric, for example for use in breathable chemical-biological protective clothing.